Recently, in clinical diagnosis/detection and analysis of the genes, immunological methods utilizing a specific interaction between specific molecules, such as an antigen and antibody thereto, and the like, are used to detect antigen, antibody, DNA (Deoxyribonucleic Acid), RNA (Ribonucleic Acid) and the like.
One of these methods, a solid phase binding assay includes a method using magnetic particles. FIG. 15 shows a schematic diagram of a solid phase assay using conventional magnetic particles.
As shown in the figure, the assay for an object 94 is carried out using a solid phase 91, a molecular receptor 95, a magnetic particle 92 and a secondary molecular receptor 93.
The solid phase 91 has a surface of the solid phase in contact with the sample solution and the molecular receptors 95 are immobilized thereto. Polystyrene beads, walls of a reaction vessel, substrates and the like are used as the solid phase 91.
The molecular receptor 95 is a substance that specifically binds to the object 94, such as antigen, antibody, DNA, RNA or the like, which exists in the sample solution. The molecular receptor 95 is such a molecule as antigen, antibody, DNA, RNA or the like, which can specifically bind to the object 94.
The magnetic particle 92 is a particle having magnetization and used as a labeling material. That is, by detecting the magnetic field formed by the magnetic particle 92, the amount of the magnetic particle 92 is determined, and the presence or absence, or concentration of an object 94 in a sample solution is determined. In addition to the magnetic particles 92, a substance that emit detectable signals, such as radioactive, luminescent and chemiluminescent materials, enzymes and the like, may be used as a label. The known assays using these labels include enzyme immunoassay (EIA) using antigen-antibody reaction, and chemiluminescent assays, such as a strictly defined chemiluminescent assay (CLIA) using an immunoassayed compound labeled with a chemiluminescent material, chemiluminescent enzyme immunoassay (CLEIA) in which enzyme activity is detected at a high sensitivity by using a chemiluminescent compound in the detection system, and the like.
The secondary molecular receptor 93 that is previously immobilized to the magnetic surface is an antibody that binds specifically to the object 94.
In the analysis shown in FIG. 15, firstly a test solution containing the object 94 is added to the solid phase 91 to which the molecular receptor 95 is immobilized beforehand. By this procedure the object 94 binds specifically. Other substances in the sample solution stay in the solution without binding to the solid phase 91. Next, the magnetic particles 92, on which the secondary molecular receptors 93 are immobilized, are added into the sample solution. By this procedure, the secondary molecular receptor 93 binds specifically to the object 94 that is bound specifically to the molecular receptor 95 immobilized onto the solid phase 91. Then, the magnetic particles 92 bound onto the solid phase is quantitated by detecting the magnetization of the magnetic particles 92. By this procedure, the concentration or the location of the object 94 bound onto the solid phase may be determined. The methods for detecting the magnetization using magnetoresistance elements disposed in array form are disclosed in the patent documents 1 and 2.
Further, the assays using these labels include sandwich assay in which the object bound specifically to the molecular receptor described above is bound specifically to another molecule label, and also competitive assay, in which the object and a different molecule label competes to bind to the molecular receptor.
Thus, in the conventional methods, signals from the label, such as light emission and the like, are detected by a device, such as an optical detection device and the like capable of detecting these signals. In these methods, it is necessary to capture signals only from the label of the molecule bound specifically to another molecule immobilized onto the solid phase. However, in the optical detection method, accurate analyses may not be carried out in the presence of unbound labeled molecules because the signals from these labels are also captured. Therefore, it is necessary to washout the unbound labeled molecules completely. Further, in the optical detection device, very weak optical signals need to be detected, which creates difficulty in making the device compact and low cost.
On the other hand, as disclosed in the patent document 1, it is not necessary to washout unbound labeled molecules in the method of detecting by the magnetoresistance element using the magnetic particles as the label. However, in a detection chip on which the magnetoresistance elements are disposed in array form, a switching circuit is needed to output the signals from each element independently. Electric interconnects are required from each element disposed in array form to the switching circuit. Therefore, this creates problems, such as difficulty in making compact and the like, because as the number of the elements are increased, the interconnects are more complicated and the more area is needed to accommodate the interconnects.
Similarly, in the detection device that detects magnetic flux in the patent document 2 described above, the detection circuit for the magnetic particles includes a bridge circuit composed of the magnetoresistance elements and transistors serving as switching elements. However, since the magnetoresistance element requires magnetic material, the steps for formation and processing of the thin magnetic film have to be carried out after a part of the circuit including the transistors is processed by a general production process for integrated circuits.
Further, the patent document 3 discloses the method for detecting magnetic particles, as in the patent document 1, by disposing the hall elements in an array-like formation.
However, in the patent document 3, the output signals of the hall elements to which the magnetic particles are not bound must be used as a standard for the output signals of the hall elements to which the magnetic particles are bound. Furthermore, since the output signal from the hall element to which the magnetic particles are bound is so small that the detection becomes difficult when the size of the magnetic particles is smaller than the size of the hall element.
The objective of the present invention is to provide a magnetic sensor, which is compact, inexpensive and with a higher detection sensitivity, and a method of measuring the amount of the magnetic particles. Further, applying this sensor and the method of measuring, the present invention provides a biosensor, which is compact, inexpensive and with higher detection sensitivity, and an assay method to analyze the objects, such as antigen, antibody, DNA, RNA and the like, by detecting the magnetism using the magnetic particles as a label, without the washout of the unbound labeling molecules.
Patent Document 1: U.S. Pat. No. 5,981,297, Description.
Patent Document 2: International Publication W097/45740, Pamphlet.
Patent Document 3: International Publication W003/67258, Pamphlet.